This invention relates to an implantable device composed of one or more bio-absorbable polymer(s) or combinations of bioabsorbable/non-absorbable polymer(s) for the repair or augmentation of connective tissue damaged by disease or injury. The devices shall serve as scaffolds for ingrowth and orientation of new fibrous connective tissue, (e.g. ligaments, tendons) in both intra-articular and extra-articular sites by maintaining structural stability during initial healing and then undergoing at least partial gradual absorption to prevent stress shielding and allow newly formed tissue to become correctly oriented and load bearing.
The invention includes several aspects of device design that are intended to provide for simulation of natural tissue function immediately after implantation and to support subsequent fibrous tissue ingrowth as well as orientation in the direction of natural loading. The devices are braided or woven into a flat tape geometry having the plurality of fibers aligned in parallel to form the axial warp. The physical/mechanical/chemical properties of all or part of the component fibers may be enhanced by a number of temperature/time/stress treatments. One or more adjacent plies of the device are used in surgery to achieve biomechanical properties approximately equivalent to the healthy tissue prior to being damaged. A swivel needle attachment system may be incorporated to facilitate handling and surgical placement of the devices. The interfibrillar space, that provides for initial tissue ingrowth, occurs as a result of the braiding/weaving process or may be enhanced by means of texturizing the yarns. Gradual bioabsorption, in whole or in part, provides for additional interfibrillar space to form during the healing period, and for fibrous tissue orientation to be induced as load is transferred from the weakened implant to the `neo-ligament` or `neo-tendon`.
The bioabsorbable materials, biocompatible nonabsorbable materials, physical and chemical combinations thereof, and the processes involved in fabricating them into the implantable devices are all included in this invention.
Ligaments and tendons are bands or sheets of fibrous connective tissue which provide support and stability to the musculoskeletal system. Relief of the pain and/or instability caused by damage to a ligament or tendon is currently achieved by techniques ranging from simple suturing to removal and replacement with other tissue or a permanent synthetic prosthesis. Although no single technique is appropriate for all situations, it is generally preferred to return the tissue to it's healthy, pre-damaged state as naturally as possible. Furthermore, it is highly desirable to reduce the need for activity restriction during the healing period. The permanent retention of implanted foreign materials is considered undesirable and should be minimized because it may result in stress shielding and subsequent atrophy of natural tissue, or the migration of the materials to other tissues and/or systems (i.e. lymphatic) may occur.
The state-of-the-art in ligament repair/reconstruction is considered to be the use of autogenous tissue grafts for augmentation or replacement of the damaged ligament. Portions of the patellar tendon, iliotibial band, semitendinosus tendon, and fascia lata are some of the most commonly used autogenous tissue grafts. Due to the undesirability of having to sacrifice one tissue and its associated function, in order to repair another, a number of synthetic, permanent total ligament prostheses and ligament augmentation implants are being tried in animals as well as clinically.
Several of the permanent ligament prostheses are fabricated so that the properties of a single synthetic material characterize the implant's response to in-vivo loading (see, e.g., U.S. Pat. Nos. 3,896,500; 3,953,896; 3,987,497; 3,988,783; and European Patent Application Nos. 51,954; 106,501; and 126,520, all of which are incorporated herein by reference). Although many of the aforementioned patents include more than one material in the structure of the body of the prosthesis, a single material determines the mechanical (tensile) properties while the secondary components are in the form of coatings, sheaths, etc. to improve biocompatibility or lubricity. While ligamentous tissue is a natural composite material exhibiting both compliant elasticity and high longitudinal strength, no single synthetic biocompatible material has this combination of properties. As a result, implants such as the ones listed above have tended to fail in animal or clinical trials either by material fatigue, creep (joint laxity), in-vivo degradation or by unacceptable restriction of joint motion.
A number of multi-component ligament prostheses (see, e.g. U.S. Pat. Nos. 3,797,047; 4,187,558; 4,483,023; and European Patent Application No. 122,744, all of which are incorporated herein by reference are more bio-mechanically compatible with the elasticity and strength requirements of natural ligament function but suffer from other shortcomings. Since they are designed to replace the natural ligament, any reparative tissue that forms at the site of the defect, is almost completely shielded from applied loads and therefore tends to resorb. The inevitable chemical and/or physical breakdown of these implants in-vivo, leads to catastrophic failure and a return to pre-operative instability, or worse, because no natural tissue repair has taken place. No ligament prosthesis, tried thus far in animals or humans, has yielded consistently acceptable joint stability without the occurence of implant breakdown, synovitis, and/or articular tissue damage during the first two years post operatively. The desired minimum post operative period of implant/joint stability is 10 years.
Attempts at a long-term `natural` tissue repair (by augmenting but not replacing the natural tissue) has been approached by the use of a variety of devices and techniques. The use of a permanent device for augmentation of an autogenous tissue transplant is described in "Experimental Mechanical and Histologic Evaluation of the Kennedy Ligament Augmentation Device", G. K. McPherson, Ph.D. et al., Clinical Orthopedics and Related Research, no. 196, pages 186 to 195, 1985, which is incorporated herein by reference. While the method of attachment allows the desired natural tissue repair to occur, the entire synthetic implant remains in situ; some interfibrillar mechanical breakdown has recently been reported, and a chronic foreign body response is observed even at 2 years following implantation. A biologically mechanically degradable augmentation device consisting of polyglycolic acid (herein abbreviated as PGA) -coated carbon fibers (U.S. Pat. No. 4,411,027) or polylactic acid (herein abbreviated as PLA) - coated carbon fibers (U.S. Pat. No. 4,329,743) has also met with limited success in obtaining a `natural` tissue ligament repair. Both of these patents are incorporated by reference. However, even though the polymer coating protects the brittle carbon fibers intra-operatively and is then safely absorbed by the body, the gross modulus and elasticity mis-match between the carbon fibers and the new ligamentous tissue that infiltrates the implant, results in fragmentation of the carbon fibers. This mechanical breakdown of the carbon fibers does serve to transfer load to the new tissue as desired, but serious concerns persist regarding the eventual disposition of the carbon fiber fragments. Finally, as described in "Acute Anterior Cruciate Ligament Injury and Repair Reinforced with a Biodegradable Intraarticular Ligament", H. E. Cabaud, M.D. et al., The American Journal of Sports Medicine, vol. 10, pages 259 to 265, 1982; and "A Partially Biodegradable Material Device for Repair and Reconstruction of Injured Tendons: Experimental Studies", W. G. Rodkey, D.V.M. et al., AAOS Meeting, 1985, both of which are incorporated herein by reference, and the comparative examples A to F herein, biodegradable implants consisting of PGA and polyester (specifically Dacron.TM.) have been tried as repair/augmentation devices for obtaining `natural` ligament and tendon healing. The results of this work indicate that PGA does not retain its properties long enough, in-vivo, and that any tissue that does infiltrate the permanent polyester fiber component does not achieve adequate strength or joint stability due to lack of tissue orientation and excessive ligament/tendon lengthening. The relatively short strength retention period of PGA, will apparently not allow the elimination of joint immobilization that is currently necessary following ligament repair or reconstruction.
The surgical repair device of this invention has functional advantages over the implant device described in European patent (hereafter EP) Application No. 122,744. For example, this invention can utilize absorbable fibers in the axial (lengthwise) direction. The majority of absorbable fibers in the axial direction enhances or essentially guarantees the transfer of the connective tissue stress from the device to the ingrowing collagen fibers. In summary, with the majority of fibers being in the axial direction and with these fibers being at least about 80% absorbable fibers, there appears to be more tissue ingrowth and better oriented collagen fibers.
This invention is useful as a temporary or augmentation device. In this utility, it seems to match as closely as possible the biological properties of a connective tissue until ingrown collagen fibers can replace the majority of fibers (preferably having an absorbable component comprising at least about 80 percent) in the axial direction. The advantage of this invention, e.g. over the implant device disclosed in EP Application No. 122,744, is that it appears to provide a surgical repair device (specifically for connective tissue, and more specifically for ligament or tendon repair) that will have the correct stress related properties to act as a connective tissue (until living tissue can replace the device). This is accomplished by the ingrown collagen fibers replacing the absorbable fibers in the axial direction. The use of nonabsorbable fibers is as a support or backbone for the absorbable fibers.
This invention has superior and unexpected structural properties over those disclosed in the prior art, specifically EP Application No. 122,744. For example, the majority of the fibers in this invention, that is 50 percent or more, are in the axial (lengthwise) direction. Preferably, 80 to 95 percent are in the axial direction. This approximately twofold increase of fibers in the axial (lengthwise) direction (over the axial direction fibers in EP Application No. 122,744) is at least one of if not the primary reason for obtaining the functional advantages discussed above.
The surgical repair device of this invention has other advantages over the prior art. For example, the thickness of the device is smaller than the known prior art devices. This is because the majority of the fibers are in the axial direction. The smaller thickness allows this device to be useful in more constricted connective tissue repair procedures. Also, as a general statement, the smaller the thickness or width of the repair device, the greater is its utility as a temporary or augmentation device because tissue ingrowth is facilitated. Conversely, the larger the thickness or width of the device, the more it is used as replacement (that is, as a permanent implant) rather than a temporary device.
It is, therefore, the object of this invention to provide sterile, surgically implantable devices, means for surgical placement/attachment, and fabrication processes that are uniquely suited for providing the most advantageous connective tissue (i.e. ligament, tendon, etc.) repair. These implants resolve the apparent disadvantages of the devices described above by: (1) providing adequate strength and stiffness immediately post-operatively to minimize or eliminate the need for immobilization; (2) facilitating the ingrowth of vascularized cellular tissue by reason of the open flat tape configuration; (3) supporting the proper orientation of collagen fibers formed within and around the implant through the predominantly axial alignment of the component yarns and the gradual transfer of applied loads from the biodegradable yarns to the newly formed tissue; (4) providing a longer lasting bioadsorbable material to permit adequate time for new tissue ingrowth or revascularization of autogenous tissue grafts or allografts; (5) providing a compliant, elastic, permanent component to protect tissues from over-load, without stress-shielding, for a longer term than provided by the bioabsorbable materials, in those applications (i.e. some intraarticular ligament reconstructions) where healing occurs more slowly; and (6) avoiding the use of materials which fragment and pose risks of migration to adjacent tissues.
The object of this invention comprises bioabsorbable or combined bioabsorbable/bicompatible polymers fabricated into an elongated textile structure having means for surgical placement/attachment at one or both ends for the purpose of repair, augmentation or replacement of damaged connective tissues, such as ligaments and tendons.